#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int numDistinct(string s, string t) {
        int m = s.size(), n = t.size();
        vector<vector<double>>dp(m + 1, vector<double>(n + 1));
        for (int i = 0; i <= m; i++)
        {
            dp[i][0] = 1;
        }
        s = ' ' + s, t = ' ' + t;
        for (int i = 1; i <= m; i++)
        {
            for (int j = 1; j <= n; j++)
            {
                dp[i][j] = dp[i - 1][j];
                if (s[i] == t[j])
                    dp[i][j] += dp[i - 1][j - 1];
            }
        }
        return dp[m][n];
    }
};